Abstract

Apical distortion product otoacoustic emissions (DPOAEs) are comprised of at least two components, as evidenced by the interference pattern of alternating maxima and minima known as fine structure. DPOAE fine structure is produced by the shifting phase relationship in the ear canal, between the generator and characteristic frequency (CF) component of the response. Each component arises from a different cochlear region and, according to theory, reflects a distinct generation mechanism. The analysis of DPOAE components and phase in newborns may provide a window into targeted aspects of cochlear physiology during development. DPOAE fine structure was recorded from 15 adults and 14 newborns using a swept-tone technique. DPOAE group delay, as well as magnitude and phase of each component, was compared between age groups. Results show narrower fine structure spacing, a longer group delay (steeper phase gradient) in low frequencies, and a stronger relative contribution from the CF component in newborns. The prolonged group delay for low-frequency DPOAEs could indicate immature basilar membrane motion in the apex of the cochlea and warrants further investigation. The enhanced contribution from the CF component may have implications for clinical practice as well as for theories of cochlear maturation.

Received 02 September 2009Revised 02 November 2009Accepted 05 November 2009Published online 05 January 2010

Acknowledgments:

This work was supported by a grant from the National Institutes of Health, NIDCD (Grant No. DC003552), the House Ear Institute, and Northwestern University. Authors would like to thank Tracy Williams and Srikanta Mishra for their assistance with data collection and management, Dr. Rangasamy Ramanathan for his continued support of neonatal hearing research at the University of Southern California Medical Center and Ping Luo for his technical assistance. Authors would also like to thank Chris Shera for his contributions with respect to phase calibration and correction. Data collection was conducted using software developed by Carrick L. Talmadge.